A plunger lift is an apparatus that is used to increase the productivity of oil and gas wells. In the early stages of a well's life, liquid loading is usually not a problem. When rates are high, the well liquids are carried out of the tubing by the high velocity gas. As the well declines, a critical velocity is reached below which the heavier liquids do not make it to the surface and start to fall back to the bottom exerting back pressure on the formation, thus loading up the well. A plunger system is a method of unloading gas in high ratio oil wells without interrupting production. In operation, the plunger travels to the bottom of the well where the loading fluid is picked up by the plunger and is brought to the surface removing all liquids in the tubing. The plunger also keeps the tubing free of paraffin, salt or scale build-up. A plunger lift system works by cycling a well open and closed. During the open time a plunger interfaces between a liquid slug and gas. The gas below the plunger will push the plunger and liquid to the surface. This removal of the liquid from the tubing bore allows an additional volume of gas to flow from a producing well. A plunger lift requires sufficient gas presence within the well to be functional in driving the system. Oil wells making no gas are thus not plunger lift candidates.
As the flow rate and pressures decline in a well, lifting efficiency declines geometrically. Before long the well begins to “load up”. This is a condition whereby the gas being produced by the formation can no longer carry the liquid being produced to the surface. There are two reasons this occurs. First, as liquid comes in contact with the wall of the production string of tubing, friction occurs. The velocity of the liquid is slowed, and some of the liquid adheres to the tubing wall, creating a film of liquid on the tubing wall. This liquid does not reach the surface. Secondly, as the flow velocity continues to slow the gas phase can no longer support liquid in either slug form or droplet form. This liquid along with the liquid film on the sides of the tubing begin to fall back to the bottom of the well. In a very aggravated situation, there will be liquid in the bottom of the well with only a small amount of gas being produced at the surface. The produced gas must bubble through the liquid at the bottom of the well and then flow to the surface. Because of the low velocity very little liquid, if any, is carried to the surface by the gas. Thus, as explained previously, a plunger lift will act to remove the accumulated liquid.
A typical installation plunger lift system 100 can be seen in FIG. 1 (prior art). Lubricator assembly 10 is one of the most important components of plunger system 100. Lubricator assembly 10 includes cap 1, integral top bumper spring 2, striking pad 3, and extracting rod 4. Extracting rod 4 may or may not be employed depending on the plunger type. Below lubricator 10 is plunger auto catching device 5 and plunger sensing device 6. Sensing device 6 sends a signal to surface controller 15 upon plunger 200 arrival at the well top. Plunger 200 is shown to represent the plunger of the present invention and will be described below in more detail. Sensing the plunger is used as a programming input to achieve the desired well production, flow times and wellhead operating pressures. Master valve 7 should be sized correctly for tubing 9 and plunger 200. An incorrectly sized master valve will not allow plunger 200 to pass. Master valve 7 should incorporate a full bore opening equal to the tubing 9 size. An oversized valve will allow gas to bypass the plunger causing it to stall in the valve. If the plunger is to be used in a well with relatively high formation pressures, care must be taken to balance tubing 9 size with the casing 8 size. The bottom of a well is typically equipped with a seating nipple/tubing stop 12. Spring standing valve/bottom hole bumper assembly 11 is located near the tubing bottom. The bumper spring is located above the standing valve and can be manufactured as an integral part of the standing valve or as a separate component of the plunger system.
Surface control equipment usually consists of motor valve(s) 14, sensors 6, pressure recorders 16, etc., and electronic controller 15 which opens and closes the well at the surface. Well flow ‘F’ proceeds downstream when surface controller 15 opens well head flow valves. Controllers operate on time, or pressure, to open or close the surface valves based on operator-determined requirements for production. Modern electronic controllers incorporate features that are user friendly, easy to program, addressing the shortcomings of mechanical controllers and early electronic controllers. Additional features include battery life extension through solar panel recharging, computer memory program retention in the event of battery failure, and built-in lightning protection. For complex operating conditions, controllers can be purchased that have multiple valve capability to fully automate the production process.
In these and other wells it is desirable to measure the downhole temperature and pressure versus time, chemical profiles and other data. This information is used to figure oil and gas reserves and production plans. Conventional methods include dropping special sensors called pressure bombs via cable down the tubing. Pressure bombs can be attached to the wireline or left downhole to be retrieved by fishing at a later date. Special trucks with a crew are used which is expensive for the well operator.
In FIG. 2 (prior art), a special truck called a wireline (also called slickline) rig 200 is used to drop a downhole equipment data logger (temperature and/or pressure and/or time) 207 down tubing 266 of the well. Nominally the tubing is two inches in diameter, and data logger 207 is about three feet long. Wireline rig 200 has an on-board computer 201 for data recording. Hoistable crane 202 supports electric line 206 which usually requires a lubricator 203 and a blowout protector 204. A spool and hoist assembly 205 controls electric line 206. All this special equipment is costly to lease for the well operator. Furthermore, the use of this equipment requires the complete shutdown of the well during the operation of dropping special data logger 207.
What is needed is an improved data logger sensor that can be dropped down a well and retrieved without a wireline rig. The plunger will house and deliver the data logger to the bottom of the well to take readings. Then the well operator can turn the well on to flow the plunger and data logger to the surface without the use of a wireline rig and crew. This sensor should be easily detachable to the plunger and readily plugged into a computer to retrieve the measured downhole temperature and/or pressure. The present invention fulfills these needs for the well operator/producer.